1. Field of the Invention
The present invention relates to a prism element, and to an observation system using the same.
2. Description of the Related Art
Conventionally, a prism element has been used in various types of optical instruments such as telescopes, observation systems and picture taking systems, as one of the optical elements for guiding incident light fluxes in a predetermined direction by reflection and collection.
Generally, in order to obtain good optical properties in an optical instrument using such a prism element, it is necessary to accurately mount the prism in a casing or to another optical member in the optical instrument.
Japanese Utility Model Publication No. 61-31290 discloses a method of mounting a prism element in which a right-angle prism is pressed to a prism sheet using a plate spring and is mounted in a casing. A combination prism constituted by a plurality of prisms is used in a binocular or the like as a roof prism for obtaining a correct image. Such a combination prism is firstly contained in a prism holder and then is pressed by a plate spring or the like so as to be mounted in the casing.
When two prisms are opposingly contained in the casing, they are opposingly disposed with a clearance of about 0.005 to 0.5 mm, and a transparent adhesive is charged into the clearance formed between the opposing surfaces of the prisms to fix both of the prisms.
In addition, a prism element is known that not only deflects incident light fluxes in a predetermined direction, but also wherein the surfaces of the prism element are formed into spherical or aspheric surfaces so as to impart thereto light collective action and image forming action. In such a prism element, it is essential to position the prism accurately so as to be stably mounted in the casing or to another optical member. However, a method of accurately positioning the prism element which includes light corrective action and image forming action has not been known.